Miniature ultrasound probes for imaging blood vessels are well known in the art (for example, see U.S. Pat. No. 4,576,177 to Webster, Jr.). In conventional imaging systems, the catheter has an outer tube containing a rotatable flexible shaft connected to an ultrasound transducer tip (see U.S. Pat. No. 4,794,931). By rotating the transducer tip, a two dimensional image slice of the blood vessel can be obtained. By linearly moving the ultrasound transducer inside the outer tube, or by moving the outer tube within the blood vessel, images of the blood vessel at various points can be obtained. The ability to image forward of the catheter tip at a controllable distance and angle in front of the tip has been either difficult or not possible.
In U.S. Pat. No. 5,174,296, an ultrasound probe is described which looks forward into a blood vessel with a pie segmented piezoelectric transducer facing forward with each segment at a different angle with respect to the rotation axis. While such a probe can produce images at different forward positions without requiring linear movement, and in a forward direction (this allows an arterial obstruction to be imaged before reaching it), the very small piezoelectric segments have limited imaging power, and therefore the ability to image clearly is reduced.